Adsorption of Lead (Pb) from Landfill Leachate onto Pruning Residues Biochar

 Landfill leachate is a highly toxic and hazardous form of wastewater due to its complex composition characteristics. Effective removal of heavy metals from landfill leachate is of great concern due to the fact that toxic metals can seriously threaten the food chain, and therefore the human health. The main objective of this work was to study the utilizing of low-cost pruning residues in the production of biochar and its application in removal of lead (Pb) from landfill leachate.

 Leachate produced in Babol municipal solid waste landfill was used as an adsorbent solution. Pruning residues were collected and used for biochar preparation. Biochar produced under the pyrolytic temperature of 700°C with a 1-hour retention time. The adsorption mechanism of pruning waste biochar to Pb was analyzed through BET surface area and scanning electron microscope (SEM) tests. Batch experiments were performed to study the effects of adsorption parameters on Pb removal. The influence of contact time (30-300 min), adsorbent dosage (1-50 g/L), as well as particle size (1-2 mm and 63-75 µm) was investigated. Moreover, the kinetic and isotherm models were applied to the experimental data to predict the adsorption parameters.

 The results obtained from the analysis of the untreated Babol landfill leachate was revealed that the Pb concentration was about 4.94 mg L-1. The surface area of the produced biochar was determined to be 292.44 m2 g-1. SEM microstructure of the biochar showed the developed surface area with visible pores. All of these data seem to suggest a great potential for pruning residues biochar to Pb removal. The adsorption of Pb was mainly affected by contact time, adsorbent dose, and biochar particle size. Higher contact time and adsorbent dosage showed higher uptake of Pb. Whereas, the uptake of Pb ions onto pruning residues biochar was substantially reduced with increase the biochar particle size. Maximum Pb percentage removal was observed at a contact time of 90 min and with an optimum biochar dosage of 20 g L-1 (89.06% removal) for biochar with 1-2 mm particle size. While, biochar with particle size of 64-75 µm can removed Pb to almost 100% at a contact time of 120 min and with an optimum biochar dosage of 20 g L-1. The kinetic study showed that adsorption can be well described by the pseudo-second order kinetic model. This supports the chemisorption theory behind the pseudo-second order kinetic model for the adsorption system. The results of isotherm models implied that the behaviors of the isotherms are more appropriate for the Langmuir model, showing a monolayer adsorption capacity for Pb.

 Findings of this research demonstrated the applicabil ity of pruning residues biochar as an economic adsorbent for the removal of the Pb from landfill leachate. On the other hand, the crop residue burning poses a threat to the environment and human health due to the emission of toxic gasses and particulate matter. So, conversion of pruning residues to biochar and its application to heavy metal removal is a useful and environment-friendly alternative to crop residue and biomass burning.